Background: betaig-h3 is an extracellular matrix protein whose expression in several cell types is greatly increased by transforming growth factor-beta (TGF-beta). TGF-beta is believed to be involved in the development of diabetic nephropathy and thus we have assessed the possibility that betaig-h3 may be a downstream molecule in this pathogenic process.
Methods: Immunoblotting and immunohistochemistry were done using an antibody against mouse betaig-h3 protein. betaig-h3 and TGF-beta concentrations were measured by enzyme-linked immunosorbent assay (ELISA). Cell adhesion and migration were assessed by measuring activity of N-acetyl-beta-d-glucosaminidase and using a transwell plate, respectively.
Results: Immunohistochemistry revealed that betaig-h3 occurs mainly in the basement membrane of proximal tubules, particularly the S3 segment but also to lesser extents in the basement membranes of the cortical thick ascending limb cells and the parietal glomerular epithelial cells in Bowman's capsule. Immunoblotting revealed that approximately 68 kD bands were seen only in the cortex + the outer stripe of the outer medulla. Rats with streptozotocin (STZ)-induced diabetes exhibited a marked and sustained increase in renal betaig-h3 abundance. This was mirrored by urinary betaig-h3 levels. In vitro experiments with human primary renal proximal tubular epithelial cells revealed that their expression of betaig-h3 was greatly increased by either TGF-beta or glucose. High glucose levels also stimulated TGF-beta production by renal proximal tubular epithelial cells and the high glucose-induced betaig-h3 expression was almost completely blocked by anti-TGF-beta antibody. betaig-h3 mediated renal proximal tubular epithelial cells adhesion and migration.
Conclusion: betaig-h3 may be important in the development of diabetic nephropathy. Furthermore, the level of urinary betaig-h3 may be useful as an early marker reflecting disease onset and progression.